1. Field of the Invention
The present invention relates to an artificial respiration apparatus and in particular, to a high-frequency oscillation (HFO) artificial respiration apparatus.
2. Description of Related Art
FIG. 11 shows a conventional HFO artificial respiration apparatus 200. An inhale gas containing a high concentration of oxygen flows from an oxygen supply port 201 via a three-way branching pipe 202 to a patient X and to an exhaust end. The inhale gas flows normally at flow rate from 10 to 30 [l/min] and 60 [l/min] at maximum, to which a high frequency oscillating air pressure is applied by an oscillating air pressure urging block 203 for oxygen supply into lungs of the patient X. Here, the average pressure applied to the lungs of the patient X is controlled by an open degree of a rubber valve of an exhale valve 204 provided at an exhaust opening of exhale gas. The oscillating air pressure has an oscillation frequency (hereinafter, referred to as ventilation frequency) adjusted by rpm of a rotary valve 206 of the oscillating air pressure urging block 203 and an amplitude adjusted by an output of a blower 205.
Here, explanation will be given on the principle of the oxygen supply in this HFO artificial respiration apparatus 200. Firstly, when the inhale gas supplied to a patient X is subjected to a HFO air pressure, the pressure amplitude of the inhale gas causes a small-amount ventilation (gas exchange like convection) with respect to the gas (hereinafter, referred to as an exhale gas) containing carbon dioxide in the lungs of the patient X and the dispersion of the inhale gas due to oscillation causes the inhale gas to enter the lungs via an in-trachea tube 207, which in turn causes the exhale gas to go out of the lungs (up to the mouth of the patient). The subsequent inhale gas performs the aforementioned ventilation and functions to send the exhale gas from the lungs to the exhale gas exhaust opening. Thus, it is possible to maintain a constant oxygen concentration in the lungs of the patient X.
The aforementioned HFO artificial respiration apparatus 200 has three basic parameters which can be set by a user (doctor) according to the state of a patient: (1) inner pressure of a patient circuit from the oxygen supply port to the patient X (5 to 15 [cmH2O] (490 to 1470 [Pa]), (2) oscillation amplitude of the high frequency oscillating air pressure (output of the blower 205), and (3) ventilation frequency of the oscillating air pressure (3 to 15 [Hz]). There are also additional parameters: the inhale gas amount supplied to a patient X and the oxygen concentration of the inhale gas. The basic parameters are controlled according to the state of the patient X so as to obtain an optimal respiration condition.
(1) When it is necessary to increase the oxygen partial pressure (PaO2) in the artery blood of the patient X, the average inner pressure of the patient circuit is increased.
(2) In order to reduce the carbon dioxide partial pressure (PaCO2) in the artery blood, the amplitude of the high frequency oscillating air pressure is increased.
(3) The inherent ventilation frequency increasing the ventilation efficiency of the HFO artificial respiration differs depending on each of the patients X as well as on the state of a patient X. Accordingly, the ventilation frequency is controlled so as to be in the vicinity of such an inherent ventilation frequency.
The ventilation frequency is initially determined by the weight of the patient X and adjusted so as to obtain resonance with the body of the patient X to increase the gas (oxygen) diffusion effect, which in turn enables to obtain an effective gas exchange (between the oxygen and the carbon oxide). In general, the ventilation frequency is set to about 15 [Hz] for new-born babies, and to 3 to 10 [Hz] for children and grown-ups.
This ventilation frequency is usually fixed to a constant value unless a sudden change of the state of the patient X is observed. Accordingly, the respiration condition is normally adjusted by the parameters (1) and (2) alone.
On the other hand, when the PaO2 is excessively reduced or the PaCO2 is excessively increased due to a change of the state of the patient X, this means that a change has occurred in the ventilation frequency inherent to the patient X and it is not sufficient to adjust the parameters (1) and (2). That is, the ventilation frequency should be adjusted.
Here, FIG. 12 shows the relationship between the ventilation frequency and the ventilation amount at a time for the lungs of the patient X when the output of the blower 205 of the oscillating air pressure urging block 203 is fixed to a drive upper limit in the HFO artificial respiration apparatus 200. As shown in FIG. 2, in the HFO artificial respiration apparatus 200, as the ventilation frequency is changed, the ventilation amount at a time is also changed. This is because a change of the ventilation frequency causes a change of the degree of the gas turbulence. For example, when the ventilation frequency is reduced, the flow resistance in the patient circuit is also reduced, and when the ventilation frequency is increased, the flow resistance is also increased.
Accordingly, in the aforementioned conventional example, if the ventilation frequency is reduced while maintaining the blower output constant, the ventilation amount at a time is abruptly increased. Even when the ventilation frequency is reduced only by 1 [Hz], the ventilation amount at a time may be excessively increased.
In order to evade this, the operator (doctor) of the HFO artificial respiration apparatus 200 should slightly reduce the output of the blower 205 by visual observation before changing the ventilation frequency. Moreover, the operator cannot know accurately how much the output of the blower 205 need be reduced. That is, it is difficult to maintain the ventilation amount at a time at a constant value when changing the ventilation frequency.
It is therefore an object of the present invention to provide a HFO artificial respiration apparatus capable of suppressing the change of the ventilation amount at a time when changing the ventilation frequency without requiring a complicated operation.
The high-frequency oscillation (HFO) artificial respiration apparatus according to the present invention comprises: an inhale gas introduction block for supplying an inhale gas containing oxygen to a patient; a patient-side path for guiding the inhale gas from the inhale gas introduction block to the patient, an oscillating air pressure urging block for applying an oscillating air pressure having a shorter cycle than a respiration cycle of the patient, to the inhale gas flowing in the patient-side path, an exhaust path for exhausting an exhale gas containing carbon dioxide exhaled from the patient; and a controller for controlling the oscillating air pressure urging block. The oscillating air pressure urging block includes an oscillation amplitude regulator for regulating an amplitude of the oscillating air pressure and a frequency regulator for regulating an oscillation frequency of the oscillating air pressure.
The controller includes an input block for accepting setting inputs for specifying an oscillation frequency of the oscillating air pressure and a ventilation amount at a time for the lungs of the patient and an operation control block for controlling the frequency regulator and the amplitude regulator according to the inputs. The operation control block has a ventilation amount maintaining function for controlling an amplitude based on the amplitude regulator in such a manner that the ventilation amount at a time for the lungs of the patient is maintained at a constant value when the oscillation frequency of the frequency regulator is changed by the setting inputs.
With this configuration, an operation of the apparatus enters an oscillation frequency of the oscillating air pressure and the ventilation amount at a time for the lungs of the patient through an external input unit connected to the input block.
The inhale gas introduced from the inhale gas introduction block is sent through the patient-side path up to the patient. The oscillating air pressure provided by the oscillating air pressure urging block is applied to the inhale gas flowing through the patient-side path. The oscillating air pressure is set to the oscillating frequency entered and the amplitude corresponding to the ventilation amount at a time for the lungs of the patient entered.
The inhale gas flows via a branching pipe into the patient-side path and to the exhaust path. The inhale gas flowing to the patient side is driven by a positive pressure of the oscillating air pressure to flow through an in-trachea insert tube into lungs of the patient to supply oxygen into the lungs. On the other hand, an exhale gas containing carbon oxide exhaled from the lungs is driven by a negative pressure of the oscillating air pressure to flow through the in-trachea insert tube into the branching pipe and is pushed into the exhaust path together with a subsequent inhale gas to be exhausted into the atmosphere.
When the patient ventilation efficiency is found to be low and the oscillation frequency is not set properly, or when the state of the patient is suddenly changed, the operator enters a new oscillation frequency value to the input block.
When the oscillation frequency is updated, the operation control block starts an operation control for modifying the oscillation frequency of the oscillating air pressure output from the oscillating air pressure urging block. Here, the operation control is performed not only for the frequency regulator but also for the amplitude regulator.
That is, according to the ventilation amount maintaining function, the operation control block performs an operation control of the amplitude regulator, so as to obtain an amplitude which does not change the ventilation amount at a time for the lungs of the patient.
According to another aspect of the present invention, the controller includes a map memory containing a map using the ventilation amount at a time for the lungs of the patient and the oscillation frequency of the oscillating air pressure as parameters for identifying an appropriate output of the amplitude regulator.
The ventilation amount at a time for the lungs of the patient and the oscillation frequency entered are used to identify a particular amplitude regulator output in the map. Moreover, when the oscillation frequency is modified, a xe2x80x9ctarget value of the oscillation frequencyxe2x80x9d and a current value of xe2x80x9cthe ventilation amount at a time for the lungs of the patientxe2x80x9d are used to identify a particular amplitude regulator output not changing the current value of the ventilation amount and an operation control is performed to set the output.
According to yet another aspect of the present invention, the map is based on test data obtained by measuring the ventilation amount at a time for the lungs of the patient while changing the output of the oscillating air pressure urging block and the oscillation frequency of the oscillating air pressure.
That is, this map is created from test data obtained by measuring the ventilation amount at a time output form the patient by the HFO artificial respiration apparatus while changing each of the output of the oscillating air pressure urging block and the oscillation frequency of the oscillating air pressure within a practical range. This test data clarifies the relationship between the output of the oscillating air pressure urging block, the oscillation frequency of the oscillating air pressure, and the ventilation amount at a time. Accordingly, when a ventilation amount and an oscillation frequency are specified, it is possible to identify a corresponding output of the amplitude regulator. That is, it is possible to know the output of the amplitude regulator to obtain a desired ventilation amount at a time and the operator can set the ventilation amount at a time for the lungs of the patient at an appropriate value.
According to still another aspect of the present invention, the apparatus further comprises an input unit connected to the controller for entering the ventilation amount at a time for the lungs of the patient and the oscillation frequency of the oscillating air pressure.
With this configuration, the operator can enter the aforementioned values through the input unit.
According to still yet another aspect of the present invention, the apparatus further comprising a display block connected to the controller for displaying a predetermined information,
wherein the operation control block has an output upper limit maintaining function, used when a target output of the oscillation regulator defined by the ventilation amount maintaining function exceeds a drive upper limit, for controlling the target output to be at the drive upper limit as well as displaying a corresponding ventilation amount at a time for the lungs of the patient on the display block.
Here, the term xe2x80x9cdrive upper limitxe2x80x9d is a value set, considering the maintenance of the amplitude regulator and does not represent a physical limit of the amplitude regulator. However, this drive upper limit may also be matched with the physical limit.
When the oscillation frequency is specified to be increased to a value under which the amplitude regulator output exceeds the upper limit in order to maintain the current ventilation amount at a time, an operation control is performed in such a manner that the output of the oscillation regulator is fixed at the upper limit.
Since the amplitude determined by the aforementioned control is not sufficient to maintain the current ventilation amount for the lungs of the patient, the ventilation amount is reduced to a value which is obtained from the oscillation regulator output and the oscillation frequency and displayed on the display block.